Run-to-run thickness uniformity often is an
issue for epitaxial reactors.
Since it is primarily affected by the way silicon is controlled and distributed,
usually it does not greatly depend on reactor design.
However, especially for single-wafer reactors, run-to-run thickness uniformity
makes reactor performance much worse than expected.

LPE
has developed a tool to significantly improve this key factor.
This patent tool, nicknamed Bubbler,
has been widely tested on LPE reactors and on reactors of other makes,
both batch and single-wafer type.

The Bubbler
cylinder is filled with liquid Chlorosilane to about 70%, while the
remaining space is the expansion space for overlying vapor.

During deposition, liquid level changes a few centimeters, so that carrier
gas saturation and mixture ratio suffer negligible changes.
Higher stability of liquid temperature is given by a large heat-exchange
surface and by a water jacket.
Usual water temperature ranges 18 to 25°C.
Correct temperature values depend on specific process requirements.LPE Thermal Regulator
has been specifically design for a high precision water temperature
control that ensure a stable temperature of the bubbler.
Therefore, for a given set-point, the relevant silicon amount delivered
to reactor is extremely constant.

For further care, liquid Chlorosilane is not refilled during deposition
or vent step, but is controlled by a purge valve of reactor (usually
the hydrogen purge valve) through the Control
Box, so as to prevent prejudicing
saturation parameters during deposition.
All this ensures higher, time-tested process reliability.